The present invention is in the field of film thickness measurement methods and film thickness measurement devices.
This invention relates to methods of measuring film thickness. More specifically, this invention relates to a capacitive measurement method useful in determining lubricant film thickness on substrates such as magnetic disks.
Perfluoropolyether lubricants currently used on magnetic thin-film rigid disks play a crucial role in protecting the head and disk surfaces. Uniformity of the lubricant film is critical for producing disks with consistent performance. Techniques to measure film thickness presently include X-ray photoelectron spectroscopy, Fourier transform infrared spectrometry, ellipsometry, and optical surface analysis. The first three such methods produce point measurements and require a substantial amount of time to properly map a surface. The fourth method, optical surface analysis, is best suited for determining a change in surface properties and is limited in vertical resolution of lubricant film thickness in comparison to other methods.
It is thus an object of the present invention to develop a method which can quickly, nondestructively, and accurately map lubricant film thickness and characterize lubricant depletion.
Although described with respect to the field of lubricant film thickness measurements, it will be appreciated that similar advantages of quick, non-destructive measurements, as well as other advantages, may obtain in other applications of the present invention. Such advantages may become apparent to one of ordinary skill in the art in light of the present disclosure or through practice of the invention.
The present invention includes capacitive film thickness measurement devices and measurement systems. The invention also includes machines or instruments using those aspects of the invention. The present invention may be used to upgrade, repair, or retrofit existing machines or instruments of these types, using methods and components known in the art. The present invention also includes methods and procedures using these devices. The methods and procedures of the present invention may be applied using procedures and protocols known and used in the arts to which they pertain.
The present invention includes a film thickness measurement device having a motion-capable platform for supporting a film-coated conductive substrate, the motion-capable platform adapted to move along a path. A conductive probe is located near the film-coated conductive substrate so as to produce a measurable capacitance therebetween. A capacitance-measuring device is adapted to measure capacitance between the film-coated conductive substrate and the conductive probe while the conductive substrate is in motion with respect to the conductive probe. The device may additionally comprise a force transducer adapted to measure friction and normal forces applied to the conductive probe. The probe may be selected from the group consisting of commercial sliders, conductive pins, and conductive pins immersed in contained liquid dielectrics. The probe may also be adapted to move along a predetermined path over a region of the motion-capable platform.
Also included in the present invention is a capacitance measurement probe comprising a conductive pin, a hollow liquid-impermeable slider housing about a portion of the pin, and a dielectric liquid contained by the hollow liquid-impermeable slider, the dielectric liquid in contact with the conductive pin. The hollow liquid-impermeable slider may be any appropriate slider such as a PTFE slider.
The present invention also includes a method for measuring film thickness. First, a film-coated conductive substrate is placed upon a motion-capable platform, the motion-capable platform adapted to move along a path. A conductive probe is then positioned near the film-coated conductive substrate so as to produce a reasonable capacitance therebetween. The motion-capable platform is then moved along the path. The capacitance is measured between the conductive probe and the film-coated conductive substrate over the path while the conductive probe is in motion with respect to the film-coated conductive substrate. The acquired measurements of capacitance are then used to calculate film thickness at each region of interest along the predetermined path.
The method for measuring film thickness may additionally comprise the step of measuring the frictional force applied to the probe over at least a portion of the path. The acquired measurements of frictional force may used along with the acquired measurements of capacitance to calculate film thickness at each region of interest along the predetermined path.
The method for measuring film thickness may additionally comprise the step of averaging capacitance measurements. The capacitance measurements may then be normalized, whereby any effect of drift in capacitance may be minimized.
The method may also comprise the step of taking an independent measurement of film thickness using an appropriate method known in the art whereby the capacitance measurements may be calibrated.
Also included in the present invention is a method for measuring film thickness. First, a film-coated conductive substrate is placed upon a rotation-capable platform. A conductive probe is positioned near the film-coated conductive substrate so as to produce a measurable capacitance therebetween, the conductive probe adapted to move radially along a vector between the axis of rotation of the film-coated conductive substrate and the outer edge of the film-coated conductive substrate. The rotation-capable platform is then rotated. The capacitance is measured between the conductive probe and the film-coated conductive substrate over at least one rotation at the current radial probe position. The conductive probe is moved radially a predetermined distance toward or away from the axis of rotation. The capacitance between the conductive probe and the film-coated conductive substrate is measured over at least one rotation at the new radial probe position. The acquired measurements of capacitance are then used to determine the thickness of the film.
The method may additionally comprise the step of measuring the frictional force applied to the probe over at least one rotation at the new radial probe position. The method may also comprise the step of continuing to move the probe in steps of the predetermined distance and measuring capacitance at those positions until all regions of interest of the film-coated conductive substrate have been measured. The capacitance measurements taken at each said radial probe position may also be averaged. The capacitance measurements taken at each said radial probe position may then be normalized, whereby the effect of drift in capacitance may be minimized.
An independent measurement of film thickness may also be taken using an appropriate method known in the art, whereby the capacitance measurements may be calibrated.
Also included in the present invention is a film thickness measurement device comprising a contained liquid dielectric and a pair of conductive probes positioned in the dielectric. The measurement device also includes at least one motion-capable fastening device, the motion-capable fastening device adapted to grasp a film in the liquid dielectric and move the film along a path between the conductive probes. A capacitance-measuring device is also included, adapted to measure capacitance between the conductive probes while the film is in motion with respect to the probes.
The film thickness measurement device may also have conductive probes that are adapted to move along a predetermined path over a region of the film. The conductive probes may be selected from the group consisting of conductive pins and substantially parallel conductive plates.
The present invention also includes a method for measuring film thickness. First, a film is placed in a contained liquid dielectric. The film is fastened to at least one motion-capable fastening device in the contained dielectric, the motion-capable fastening device adapted to move the film along a path. A pair of conductive probes is placed near to and on opposing sides of the film so as to produce a reasonable capacitance therebetween. The film is then moved along the path. The capacitance is measured between the conductive probes while the film is in motion with respect to the conductive probes. The acquired measurements of capacitance are then used to calculate the thickness of the film at each region of interest along the path.
The method for measuring film thickness may additionally comprise the step of averaging the capacitance measurements. The method may also comprise the step of normalizing capacitance measurements, whereby any effect of drift in capacitance may be minimized.
The method may also include the step of taking an independent measurement of film thickness using an appropriate method, whereby the capacitance measurements may be calibrated.